Integrated electro-optic hybrid communication system

ABSTRACT

A system according to embodiments of the invention may comprise a first communication path that converts an optically-modulated source signal to a radio signal based on a detected degradation in a quality of a received optical signal, and a second communication path that converts a radio-modulated source signal to an optical signal based on a detected degradation in a quality of a received radio signal. The system may therefore adapt to diverse weather conditions to improve the reliability of a communication link.

TECHNICAL FIELD

The present invention relates generally to communication systems, andmore particularly to a communication system which combines optical andelectrical transmitting and receiving capabilities to provide a highlyreliable communication link in diverse weather conditions.

BACKGROUND OF THE INVENTION

Communications systems have seen exponential growth in demand forbandwidth by the large and small business communities. Moreover,businesses demand a high level of availability in the communicationsystems. One known measure of availability which communication servicesproviders strive to sustain is “five nines” availability, wherein acommunication link may be down for only a few minutes a year.

Free space optics (FSO) and broadband radio are two technologies thathave been proposed to meet the demand for bandwidth. FSO, however, whileproviding “infinite” bandwidth, has some drawbacks. For instance, fogmay disperse the light beam, thereby rendering reception impossible forlong haul communication. Accordingly, for five nines availability, FSOis primarily used for short links (less than 1.5 km). In Europe, forexample, FSO has been deployed for applications such as short hops.

Broadband radio technology, on the other hand, is not hampered by fog asis FSO, and accordingly is more reliable for long haul communication.However, heavy rain tends to degrade radio performance. FSO performance,by contrast, is not as quickly degraded by heavy rain.

In view of the foregoing considerations, a system is called for toaddress the growing demand for bandwidth along with a high level ofavailability in communication systems.

SUMMARY OF THE INVENTION

Embodiments of the present invention relate to a “hybrid” communicationsystem that includes a combination of radio and optical elements. Thesystem may comprise a hybrid transmit path that converts anoptically-modulated source signal to a radio signal based on a detecteddegradation in a quality of a received optical signal, and a hybridtransmit path that converts a radio-modulated source signal to anoptical signal based on a detected degradation in a quality of areceived radio signal. The respective hybrid transmit paths may alsofunction as corresponding hybrid receive paths for received signals. Thesystem may communicate with another system of substantially the samekind to inform the other system when hybrid paths are being used, and toinstruct the other system to transmit correspondingly in return.

The system may further comprise optical-only transmit and receive paths,and radio-only transmit and receive paths. The system is therefore ableto receive and transmit an optical signal under conditions that are morefavorable to the optical signal than to a radio signal, and receive andtransmit a radio signal under conditions that are more favorable to theradio signal than to the optical signal. But, the system is further ableto adapt to diverse weather conditions, by forming hybrid transmit andreceive paths depending on the conditions. For example, in foggyconditions, the system could convert an optically-modulated sourcesignal to a radio signal and transmit the radio signal, and instructanother system to transmit a radio signal in return. Thus, communicationbetween the two systems would be via radio signals, which are notadversely affected by fog in a significant way. Alternatively, in heavyrain, the system could convert a radio-modulated source signal to anoptical signal and transmit the optical signal, and instruct anothersystem to transmit an optical signal in return. Thus, communicationbetween the two systems would be via optical signals, which are notadversely affected by heavy rain in a significant way. Accordingly, acommunication link that uses the system may be reliably maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a hybrid radio/optical communication system according toembodiments of the invention;

FIG. 2 shows another possible embodiment of a hybrid radio/opticalcommunication system according to the invention;

FIG. 3 shows detail of a control circuit according to embodiments of theinvention;

FIG. 4 shows detail of a radio transceiver according to embodiments ofthe invention;

FIG. 5 shows detail of an optical transceiver according to embodimentsof the invention; and

FIG. 6 shows a process flow according to embodiments of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a communication apparatus according to embodiments of theinvention. The apparatus may comprise a system 100 and a system 101 thatmay communicate with each other. System 100 and system 101 may besubstantially identical, and therefore only system 100 will be discussedin detail. In an overall communication network setting, system 100 andsystem 101 could differ from each other in that one system could havecontrol over some operations of the other system. For example, system100 could be a “local” or “control” system while system 101 was a“remote” system having some aspects of its operations controlled bysystem 100.

System 100 may be configured to receive and transmit both opticalsignals and radio signals. System 100 may provide transmit and receivecommunication paths that are optical-only, radio-only, or a “hybrid” ofoptical and radio. More particularly, system 100 may provide a transmitpath for a source signal that is optically modulated and transmittedusing optical transmitting equipment, and may provide a transmit pathfor a source signal that is radio modulated (i.e., uses radiomodulation) and is transmitted using radio transmitting equipment. Onthe other hand, if a degradation in a quality of a received opticalsignal is detected, a transmit path through system 100 for theoptically-modulated source signal may be formed which originates inoptical modulating equipment but subsequently uses radio transmittingequipment, creating a hybrid optical-to-radio transmit path.Alternatively, if a degradation in a quality of a received radio signalis detected, a transmit path through system 100 for the radio-modulatedsource signal may be formed which originates in radio modulatingequipment but subsequently uses optical transmitting equipment, creatinga hybrid radio-to-optical transmit path. The hybrid transmit paths thusformed may also function as corresponding hybrid receive paths.

System 100 may comprise a coupler 102 that connects a source 120 to anoptical modulator/demodulator 103. Source 120 could provide voice, dataor video, for example. Modulator/demodulator 103 may include a telemetrycircuit via which a “handshake” comprising control and status signalsmay be exchanged with system 101. A received optical signal may also becoupled by coupler 102 to a control circuit 106 for detectingdegradation in a quality of the received optical signal and causing ahybrid optical-to-radio transmit path to be formed in response, asdiscussed in more detail below. Modulator/demodulator 103 opticallymodulates a laser 104 with source signal 120. The modulated signal maythen be input to an optical signal splitter 105 which splits themodulated signal into two separate identical signals, forming a firstoutput and a second output of the optical signal splitter 105. Opticalsignal splitter 105 may comprise mirrors. The mirrors may, for example,be discrete mirrors, or be fabricated on a GaAs substrate usingmicrowave monolithic integrated circuit (MMIC) technology.

The first output of optical signal splitter 105 may be input to a firstswitch, SW1, and the second output of optical signal splitter 105 may beinput to a second switch, SW2. Typically, under circumstances which aremore favorable to communication via an optical signal than tocommunication via radio, SW2 would be open and SW1 would be closed.Control circuit 106 may control which of SW1 and SW2 is open and whichis closed. SW1 and SW2 may be non-reflective switches.

The output of SW1 may be connected to a first input of an opticalswitch, SW A. SW A may be a single-pole-double-throw optical switch. Theoutput of SW A may be connected to an optical transceiver 107 fortransmitting or receiving an optical signal. The output of SW2 may beconnected to an optical-to-electrical signal converter 114 forconverting an optical signal to a radio signal. Optical-to-electricalsignal converter 114 may also function as an electrical-to-opticalsignal converter for a received radio signal. The connection of SW2 tooptical-to-electrical signal converter 114 may be via an optical fibermedium. Optical-to-electrical signal converter 114 may be connected to afirst input of an electrical switch, SW B. SW B may be asingle-pole-double-throw electrical switch. The output of SW B may beconnected to a radio transceiver 111 for transmitting or receiving aradio signal.

System 100 may further comprise a coupler 108 that connects a source 125that provides, e.g., voice, data or video, to a radiomodulator/demodulator 109. A received radio signal may also be coupledby coupler 108 to a control circuit 113 for detecting degradation in aquality of the received radio signal and causing a hybridradio-to-optical transmit path to be formed in response, as discussed inmore detail below. The modulated signal from modulator/demodulator 109may be input to a radio signal splitter 110 which splits the modulatedsignal into two separate identical signals, forming a first output and asecond output of the radio signal splitter 110. Radio signal splitter110 may be a 90-degree splitter.

The first output of radio signal splitter 110 may be input to a thirdswitch, SW3, and the second output of radio signal splitter 110 may beinput to a fourth switch, SW4. Typically, under circumstances which aremore favorable to communication via radio than to communication via anoptical signal, SW3 would be open and SW4 would be closed. SW3 may becoupled to a terminator 112 to prevent reflections back to the inputsource. Control circuit 113 may control which of SW3 and SW4 is open andwhich is closed. SW3 and SW4 may be non-reflective switches.

The output of SW3 may be connected to an electrical-to-optical signalconverter 115 for converting a radio signal to an optical signal.Electrical-to-optical signal converter 115 may also function as anoptical-to-electrical signal converter for a received optical signal.The connection of SW3 to electrical-to-optical signal converter 115 maybe via a coaxial cable. Electrical-to-optical signal converter 115 maybe connected to a second input of SW A. The output of SW4 may beconnected to a second input of SW B.

Reference numeral 130 represents optical signals being transmitted andreceived by optical transceiver 107 and an optical transceiver of system101. Reference numeral 135 represents radio signals being transmittedand received by radio transceiver 111 and a radio transceiver of system101. A received optical signal may travel one of the communication pathsdescribed above, but in the opposite direction from a transmitted sourcesignal. That is, a received optical signal could travel an optical-onlyreceive path or a hybrid optical-to-radio receive path, depending on thestates of switches SW A, SW B and SW1-SW4. For example, in anoptical-only receive path, SW1 could be closed, SW2 could be open, andSW A could be connected to SW1. In this arrangement, a received opticalsignal would travel from optical transceiver 107 through SW A, SW1 andoptical signal splitter 105, to be demodulated by opticalmodulator/demodulator 103. The demodulated signal would then be coupledby coupler 102 to control circuit 106, which may be configured to detectdegradation in a quality of the received optical signal and cause ahybrid optical-to-radio transmit path to be formed in response, asdiscussed in more detail below.

On the other hand, SW2 could be closed, SW1 could be open, and SW Bcould be connected to optical-to-electrical converter 114 to form ahybrid radio-to-optical receive path. In this arrangement, a receivedradio signal would travel from radio transceiver 111 through SW B, andbe converted to an optical signal by converter 114. The convertedreceived signal would then travel through SW 2 and splitter 105 to bedemodulated by modulator/demodulator 103. The demodulated signal wouldthen be coupled by coupler 102 to control circuit 106 to detectdegradation in a quality of the received radio (now converted tooptical) signal.

Symmetrically, a received radio signal could travel a radio-only receivepath or a hybrid optical-to-radio receive path, depending on thestatuses of switches SW A, SW B and SW1-SW4. For example, in aradio-only receive path, SW4 could be closed, SW3 could be open, and SWB could be connected to SW4. In this arrangement, a received radiosignal would travel from radio transceiver 111 through SW B, SW4 andradio signal splitter 110, to be demodulated by radiomodulator/demodulator 109. The demodulated signal would then be coupledby coupler 108 to control circuit 113, which may be configured to detectdegradation in a quality of the received radio signal and cause a hybridradio-to-optical transmit path to be formed in response, as discussed inmore detail below.

On the other hand, SW3 could be closed, SW4 could be open, and SW Acould be connected to electrical-to-optical converter 115 to form ahybrid optical-to-radio receive path. In this arrangement, a receivedoptical signal would travel from optical transceiver 107 through SW A,and be converted to a radio signal by converter 115. The convertedreceived signal would then travel through SW 3 and splitter 110 to bedemodulated by modulator/demodulator 109. The demodulated signal wouldthen be coupled by coupler 108 to control circuit 113 to detectdegradation in a quality of the received optical (now converted toradio) signal.

FIG. 3 shows details of one possible embodiment of a circuit that couldbe used to implement control circuits 106 and 113 for detectingdegradation in a received optical signal and a received radio signal,respectively, and causing a corresponding hybrid transmit/receive pathto be formed in response. For example, control circuit 106 (arbitrarilydesignated “A” for purposes of illustration) could comprise anoperational amplifier 303 which outputs a difference signal 316. Inputsto operational amplifier 303 could include a reference signal-to-noise(S/N) voltage signal 304 and received optical signal 305, coupled tocontrol circuit 106 by coupler 102 as shown in FIG. 1. Received opticalsignal 305 could be processed by a detector/amplifier 314 before beinginput to operational amplifier 303. Difference signal 316 could be inputto a flip-flop 302 with outputs Q 306 and /Q (Q complement) 307. Asshown in FIG. 1, Q 306 may be connected to switch SW1 and /Q 307 may beconnected to switch SW2. Thus, a change in state of Q 306 and /Q 307could, for example, cause switch SW1 to open and switch SW2 to close, orvice versa. Also, as shown in FIG. 1, Q 306 could be input to SW B sothat a change in state of Q 306 could cause SW B to select a differentinput. Flip-flop 302 could also have a clock input 317, generated by asystem internal oscillator 300 coupled to a oneshot circuit 301 foradjusting the clock pulse width.

Difference signal 316 could indicate a degradation in the quality ofreceived optical signal 305. That is, if a difference between receivedoptical signal 305 and reference signal-to-noise (S/N) voltage signal304 was less than a predetermined threshold amount or level, the qualityof received optical signal 305 could be considered to be acceptable. Onthe other hand, if a difference between received optical signal 305 andreference signal-to-noise (S/N) voltage signal 304 was greater than apredetermined threshold amount or level, the quality of received opticalsignal 305 could be considered to be unacceptable.

More particularly, a difference between received optical signal 305 andreference signal-to-noise (S/N) voltage signal 304 could be small enoughthat difference signal 316 was equivalent to a logic “0” when input toflip-flop 302. While difference signal 316 remained at a logic “0”level, the clock input 317 would not cause any change in the Q 306 and/Q 307 outputs of flip-flop 302. Assuming that SW1 was closed, SW2 wasopen and that SW A was connected to SW1, system 100 would provideoptical-only transmit and receive paths for source 120 and for receivedinput signal 305, respectively.

On the other hand, the quality of received optical signal 305 could bedegraded to the extent that a difference between received optical signal305 and reference signal-to-noise (S/N) voltage signal 304 could becomelarge enough that difference signal 316 would change from the equivalentof a logic “0” to the equivalent to a logic “1” when input to flip-flop302. In that event, the values of Q 306 and /Q 307 would “flip”; i.e.,be reversed, causing switch SW1 to open, switch SW2 to close and SW B toselect the input from optical-to-electrical signal converter 114. Byclosing SW2, the output of optical modulator/demodulator 103 would beconverted to a radio signal by optical-to-electrical signal converter114 and transmitted by radio transceiver 111. At substantially the sametime, system 100 would exchange a handshake with system 101, i.e.,exchange pre-arranged telemetry signals with system 101. The handshakewould inform system 101 that system 100 had formed a hybridoptical-to-radio transmit path for source 120 and instruct system 101 tostop transmitting optical signals to system 100 and instead begintransmitting radio signals to system 100. The hybrid optical-to-radiotransmit path formed by system 100 would also function as a hybridradio-to-optical receive path for a received radio signal from system101. Therefore, based on the handshake, system 101 would begintransmitting a radio signal to system 100, for example, by forming ahybrid optical-to-radio transmit path or a radio-only transmit path. Thepaths thus formed by system 101 would also function as receive paths forthe radio signals now being transmitted by system 100.

Control circuit 106 could further include a bandwidth adjust signal 319for adjusting the bandwidth of the radio signal, in the event that theoptical data source has a bandwidth or capacity that is greater than thebandwidth or capacity of the radio/antenna.

Control circuit 113 (arbitrarily designated “B” for purposes ofillustration) may be symmetrical to control circuit 106. Control circuit113 could comprise an operational amplifier 308 which outputs adifference signal 318. Inputs to operational amplifier 308 could includea reference signal-to-noise (S/N) voltage signal 309 and a receivedradio [input] signal 310, coupled to control circuit 113 by coupler 108as shown in FIG. 1. Received radio signal 310 could be processed by adetector/amplifier 315 before being input to operational amplifier 308.Difference signal 318 could be input to a flip-flop 313 with outputs Q311 and /Q 312. As shown in FIG. 1, Q 311 may be connected to switch SW4and /Q may be connected to switch SW3. Thus, a change in state of Q 311and /Q 312 could, for example, cause switch SW4 to open and switch SW3to close, or vice versa. Also, as shown in FIG. 1, Q 311 could be inputto SW A so that a change in state of Q 311 could cause SW A to select adifferent input. Flip-flop 313 could also have clock input 317.

Difference signal 318 could indicate a degradation in the quality ofreceived radio signal 310. In the event of such a degradation, a changein the transmit path for source 125 could be effected to switch from aradio-only path and to instead use a hybrid radio-to-optical path of thesystem 100. That is, upon difference signal 318 changing to an extentthat an unacceptable level of radio signal degradation has occurred, theQ 311 and /Q 312 outputs of flip-flop 313 may change states. Assumingthat SW4 had been closed, SW3 had been open and SW B had the input fromSW4 selected before the change in state, by closing SW3 and causing SW Ato select the input from electrical-to-optical converter 115, the outputof radio modulator/demodulator 109 would be converted to an opticalsignal by electrical-to-optical signal converter 115 and transmitted byoptical transceiver 107. At substantially the same time, system 100would exchange a telemetry handshake with system 101 to cause system 101to adapt accordingly. The hybrid radio-to-optical transmit path formedby system 100 would also function as a hybrid optical-to-radio receivepath for a received optical signal from system 101. Thus, based on thehandshake, system 101 would begin transmitting a radio signal to system100, for example, by forming a hybrid radio-to-optical transmit path oran optical-only transmit path. The paths thus formed by system 101 wouldalso function as receive paths for the optical signals now beingtransmitted by system 100.

Clearly, in view of the above-described embodiments, if following aswitch from either an optical-only path to a hybrid optical-to-radiotransmit path and corresponding hybrid radio-to-optical receive path, orfrom a radio-only to a hybrid radio-to-optical transmit path andcorresponding hybrid optical-to-radio receive path, received signalquality improved to the point that it was no longer below thepredetermined threshold level, a switch could be performed back from therespective hybrid paths to either an optical-only path or a radio-onlypath.

FIG. 6 shows a process flow according to embodiments of the invention.Assume, initially, an optically-modulated source signal transmitted byfirst system according to embodiments of the invention, and an opticalsignal received by the first system from a second system according toembodiments of the invention. As shown in block 600, a first system maytransmit the source signal to the second system using an optical-onlytransmit path, and receive the optical signal from the second systemusing an optical-only receive path. The first system may monitor aquality of the received optical signal, to determine whether the qualityof the received optical signal is below a predetermined threshold level,as shown in block 601.

If the result of the determination of block 601 is that the quality ofthe received optical signal is not below the predetermined thresholdlevel, the first system may continue to transmit and receive using anoptical-only path. On the other hand, if the result of the determinationof block 601 is that the quality of the received optical signal is belowthe predetermined threshold level, the first system may form a hybridtransmit path, as described above, for the source signal that convertsthe source signal into a radio signal which is transmitted to the secondsystem, as shown in block 602. The transmit path thus formed may alsofunction as a corresponding hybrid receive path for a radio inputsignal, as described above. At substantially the same time, the firstsystem may instruct the second system to stop transmitting an opticalsignal to the first system and instead transmit a radio signal to thefirst system, as shown in block 603.

The first system may then transmit and receive using the hybrid path fora period of time, as shown in block 604. The first system may monitor aquality of the received radio signal, to determine whether the qualityof the received radio signal is below a predetermined threshold level,as shown in block 605. If the result of the determination of block 605is that the quality of the received radio signal is not below thepredetermined threshold level, the first system may continue to transmitand receive using an optical-only path. On the other hand, if the resultof the determination of block 605 is that the quality of the receivedradio signal is below the predetermined threshold level, the firstsystem may again form a transmit path for the source signal that isoptical-only, as shown in block 606. At substantially the same time, thefirst system may instruct the second system to stop transmitting a radiosignal to the first system and instead transmit an optical signal to thefirst system, as shown in block 606. The first system may then transmitand receive using an optical-only path for a period of time. Theforegoing process may be repeated a plurality of times.

A completely parallel process to the process described above could beperformed, of course, initially assuming a radio-modulated source signaltransmitted by a first system, and a radio signal received by the firstsystem from a second system. Further, in response to the instructionsfrom the first system, the second system may also form hybrid transmitand receive paths, or change from hybrid paths back to optical-only orradio-only paths.

In view of the above-described structures and processes, a system andmethod according to embodiments of the invention enable a highlyreliable communication link that is adaptable to diverse weatherconditions. For example, a first system and a second system according toembodiments of the invention might both have optically-modulatedsources, and exchange optical signals for a period of time. Then, due tochanging weather conditions (for example, the occurrence of heavy fog),the first system might detect a degradation in the quality of itsreceived optical signal. Accordingly, the first system would form ahybrid optical-to-radio transmit path for its source, and atsubstantially the same time, instruct the second system to do the same.The hybrid optical-to-radio transmit paths thus formed would alsofunction as corresponding hybrid radio-to-optical receive paths. Thefirst and second systems might then transmit and receive via radiosignals for a time. The respective optically-modulated sources of thefirst and second systems would not be affected by the formation of thehybrid paths.

Then, possibly, due to changing weather conditions (for example, theoccurrence of heavy rain), the quality of the radio signals exchanged bythe first and second systems could degrade. In that event, the firstsystem could switch back to optical-only transmit and receive paths, andinstruct the second system to do the same. The first and second systemsmight then transmit and receive via optical signals for a time, untilthe quality of the optical signals degraded again, and so on.

A completely parallel process to that described in the foregoing is alsoreadily envisaged, assuming a first system and a second system accordingto embodiments of the invention both having radio-modulated sources.However, the first and the second systems need not necessarily have likesources. For example, a first system could have a source that wasoptically modulated, while a second system could have a source that wasradio-modulated. By means of a suitable handshake, i.e., by an exchangeof pre-arranged telemetry signals between the first system and thesecond system, either system could be caused to form a suitable hybridpath to communicate with the other system. For example, the first systemcould form a hybrid optical-to-radio transmit path and correspondinghybrid radio-to-optical receive path, while the second system utilizedradio-only transmit and receive paths. Alternatively, the first systemcould utilize optical-only transmit and receive paths while the secondsystem could form a hybrid radio-to-optical transmit path andcorresponding hybrid optical-to-radio receive path. Of course, theforegoing permutations could also be realized with the roles of thefirst and second systems reversed.

FIG. 2 shows alternative embodiments to systems 100 and 101. FIG. 2shows systems 200 and 201 which are identical to systems 100 and 101,respectively, except that switches SW1, SW2, SW3 and SW4 are notincluded. Instead, the Q and /Q signals from control units 106 and 113may be coupled directly to switches SW A and SW B. The Q and /Q signalsmay control whether SW A will receive an “unconverted” optical signaldirectly from optical signal splitter 105, or whether SW A will receiveda “converted” optical signal; i.e., a signal which has been convertedfrom a radio signal to an optical signal by electrical-to-opticalconverter 115. Symmetrically, the Q and /Q signals may control whetherSW B will receive an “unconverted” radio signal directly from radiosignal splitter 110, or whether SW B will received a “converted” radiosignal; i.e., a signal which has been converted from an optical signalto a radio signal by optical-to-electrical converter 114. Depending onwhich of SW A and SW B is currently carrying the input signal, thetransceiver connected to the other switch may be placed in a stand-bymode. That is, if SW A is currently carrying the input signal, radiotransceiver 111 may be placed in stand-by mode, and if SW B is currentlycarrying the input signal, optical transceiver 107 may be placed instand-by mode. By eliminating switches SW1-SW4 as shown in FIG. 2, asystem 200 may be constructed more inexpensively, and may operate morereliably.

FIG. 4 shows one possible implementation of radio transceiver 111according to embodiments of the invention. Radio transceiver 111 may bea standard duplex broadband radio unit. Its transmit path may comprisean AGC (automatic gain control) circuit 400 coupled to a “doubleconversion front end” comprising a mixer 401 followed by a band-passfilter 402, an amplifier 403, a mixer 404 and a band-pass filter 405.The band-pass filter 405 may be coupled to a pre-driver 406 which iscoupled to a power amplifier 407. Power amplifier 407 may be coupled toa diplexer 408 which is in turn coupled to an antenna 409.

Generally, ACG circuit 400 may compensate for losses due to cabling andconnectors from SW B. The double conversion front end may translate theIF frequency to the final transmission frequency. Pre-driver 406 andpower amplifier 407 amplify the output signal to the desired signallevel for over-the-air transmission through antenna 409. Diplexer 408may contain the transmit band-pass filter for grooming the transmitteroutput spectrum. Synthesizer 417 may be input to mixers 401 and 405 andmay provide local oscillator signals for up-conversion to the desiredtransmitter frequency.

The receive path of radio transceiver 111 may comprise antenna 409 anddiplexer 408, which may contain the receive band-pass filter. Diplexer408 may be coupled to a low-noise amplifier 410, which may in turn becoupled to a “double conversion down converter” comprising a mixer 411followed by a band-pass filter 412, an amplifier 413, a mixer 414 and aband-pass filter 415. Band-pass filter 414 may be coupled to an AGCcircuit 416 which is input to SW B. AGC circuit 416 may compensate forreceiver input variations. Synthesizer 417 may be input to mixers 411and 414 and provide local oscillator signals for RF frequencydown-conversion to an IF signal. The IF signal may be sent via SW Bthrough system 100 for demodulation and data extraction.

According to embodiments, radio transceiver 111 may further comprisesuch features as a built-in temperature sensor, a voltage standing waveratio (vswr) monitor, a receive signal level (RSL) indicator, and atransmit power monitor.

FIG. 5 shows one possible implementation of optical transceiver 107according to embodiments of the invention. The transmit path of opticaltransceiver 107 may comprise a divergence select module 500 followed bya point-ahead beamsteerer 501, a transmit/receive isolation filter 503,a track beamsteerer 504, and a gimbal 506 and telescope 507. The receivepath of optical transceiver 107 may comprise telescope 507, followed bytrack beamsteerer 504, transmit/receive isolation filter 503, receiveoptics filter 508, bifurcating mirror 509, acquisition detector 510,gimbal 506, a command/track detector 512, and acquisition and trackcontrol electronics 511. A control processor 513 may control operationsof optical transceiver 107 based on input signals such as a positionfeedback signal from gimbal 506, an acquisition detection signal and atrack error signal from acquisition and track control electronics 511,and a point-ahead feedback signal from a point-ahead detector 502.Control processor may output control signals such as a track commandsignal to gimbal 506, a scan and point-ahead command to point-aheadbeamsteerer 501, and a divergence select signal to divergence selectmodule 500.

In a transmit mode of operation, divergence select module 500 mayreceive an optical input signal from SW A. A divergence select signalfrom control processor 513 may select a beam divergence. The opticalbeam may then be directed to transmit/receive isolation filter 503.Track beamsteerer 504 may focus the beam on telescope 507, which maythen beam the optical signal to a remote site.

In a receive mode of operation, telescope 507 may receive an opticalsignal from a remote site, directing it to track beamsteerer 504 andfrom there to transmit/receive isolation filter 503. The filtered signalmay undergo further filtering, and be split into two optical signals.One of the two optical signals may go to command/track detector 512 andthe other to acquisition detector 510. The output of command/trackdetector 512 may be sent via SW B through system 100 for demodulation.The output of acquisition detector 510 may be sent to acquisition andtrack control electronics 511, which may provide the track error andacquisition detection signals which are fed to control processor 513.

According to embodiments, radio modulation for the source signal may be16 QAM, 32 QAM, 64 QAM or another type of modulation, such as QPSK.Optical modulation of the source signal may be on/off keying-typemodulation or another type of modulation.

Embodiments of the invention as described above may find usefulapplication in, for example, point-to-point, point-to-multipoint, meshand star system configurations.

Several embodiments of the present invention are specificallyillustrated and/or described herein. However, it will be appreciatedthat modifications and variations of the present invention are coveredby the above teachings and within the purview of the appended claimswithout departing from the spirit and intended scope of the invention.

1. A system comprising: a first communication path configured tomodulate a source signal optically and transmit said optically-modulatedsource signal using an optical signal transmitter; a secondcommunication path configured to modulate a source signal optically andtransmit said optically-modulated source signal using a radio signaltransmitter; a third communication path configured to modulate a sourcesignal using radio modulation and transmit said radio-modulated sourcesignal using a radio signal transmitter; and a fourth communication pathconfigured to modulate a source signal using radio modulation andtransmit said radio-modulated source signal using an optical signaltransmitter; wherein said first and second communication paths comprisean optical signal splitter that splits said optically-modulated sourcesignal into first and second optical signals; and wherein said firstoptical signal is coupled to an optical switch coupled to an opticaltransceiver, and said second optical signal is coupled to anoptical-to-electrical converter coupled to an electrical switch coupledto a radio transceiver.
 2. The system of claim 1, wherein said opticalswitch is switchable between said first optical signal and anelectrical-to-optical converter of said third communication path.
 3. Asystem comprising: a first communication path configured to modulate asource signal optically and transmit said optically-modulated sourcesignal using an optical signal transmitter; a second communication pathconfigured to modulate a source signal optically and transmit saidoptically-modulated source signal using a radio signal transmitter; athird communication path configured to modulate a source signal usingradio modulation and transmit said radio-modulated source signal using aradio signal transmitter; and a fourth communication path configured tomodulate a source signal using radio modulation and transmit saidradio-modulated source signal using an optical signal transmitter;wherein said third and fourth communication paths comprise a radiosignal splitter that splits said radio-modulated source signal intofirst and second radio signals; and wherein said first radio signal iscoupled to an electrical-to-optical converter coupled to an opticalswitch coupled to an optical transceiver, and said second radio signalis coupled to an electrical switch coupled to a radio transceiver. 4.The system of claim 3, wherein said electrical switch is switchablebetween said second radio signal and an optical-to-electrical converterof said second communication path.